The color image processing apparatus optically reads color image information on a document, identifies the information as one of predetermined multiple colors including black, red and blue, and record a color image on a record sheet on the basis of the information by using a color recording device. This type of color image processing apparatus is disclosed in Japanese Patent Publication Open to Public Inspection Nos. 147374/82 and 62769/83.
FIG. 76 shows part of a key assembly of the said color image processing apparatus.
In this figure, color image information is separated into white and cyan colors, each of which is projected onto image sensors 104 and 105 for electrophotographic conversion.
More specifically, white and cyan color signals are supplied to the subtracter 2 where red color is separated. These white, cyan and red colors are gain-controlled by the AGC circuits 3, 4 and 5, respectively, and then are coded by the binary coding circuits 6, 7 and 8, respectively. The coded output is again converted into red and black color signals by the arithmetic circuit 9, for example, and these signals are supplied to the color copying machine as image signals for color reproduction of the original.
With a color image processing apparatus capable of recording such a color image, when subjecting an image signal undergone photoelectric conversion to various processing such as resolution correction, and enlarging/reducing, it is necessary to provide processing means per color identified by color separation means or color discrimination means. More specifically, as shown in FIGS. 77 and 78, one image processing circuit is required per color signal, disadvantageously resulting in increased cost, as well as a large processing circuit.
Japanese Patent O.P.I. Publication No. 163980/1984 described a technique for representing the image signal reading using color codes.
This patent, however, merely describes a technique for converting an image signal into color codes, and discloses nothing about an effective image processing based on color codes.
Additionally, this technique incurs another problem: the image signal does not contain data indicating image density, and density processing is impossible.
There is another color image processing technique where a specific region on a document designated with a marker of a specific color is detected, and the so-detected are is subjected to a specific image processing operation.
For example, as shown in FIG. 79, once a portion of a black-and-white document is marked with a colorant of a specific color (for example, red), the image information on inside the color-marked region is recorded as converted from black into red that is a color of the marker.
Japanese Patent O.P.I. Publication Nos. 89371/1982 and 196658/1982 discloses apparatuses that are capable of detecting a marker-designated region.
These apparatuses discriminates and read a color different from that of a document, and photoelectrically convert it to generate an image signal, thereby based on the image signal, the apparatuses detect a region defined by a color marker. These apparatuses can discriminate and read a region that has a color different from that of a document, wherein the apparatuses feed an image signal based on the so-separated information, and detect a marker-designated region.
With these apparatuses, however, the so-separated information does not include color information, and the image signal photoelectrically converted from the separated information. Accordingly, there is a problem; the apparatuses can read only one specific color different from that of a document.
According to the present invention, to solve the problem, an image being read is identified to one particular color selected from a plurality of specific colors, and is converted into an image signal comprising pixels individually assigned to a color code representing a specific color, thereby based on the color codes, a marker-designated region and the associated color are detected, and the image signal is processed. Correspondingly, the technique of the invention is capable of designating regions with markers of plural colors, and of detecting the regions, and, at the same time, the technique is capable of simultaneously detecting the designated region based on the color codes and performing another process such as data processing on the image density.
The "pixel" in the current description is a minimum unit associated with image signal reading. When used in relation to a solid state image reading element, a pixel is one of a plurality of pixel arrayed in one line.
The invention further relates to a method of image processing with improvements of increasing resolution for image signal and an apparatus to implement the method.
FIG. 80 presents an example of the configuration of an image pickup unit for the image processing apparatus. According to the configuration, the manuscript or document 2 on the platen glass 1 is scanned by the exposure light source 5 installed on the carriage travelling on the slide rail 3. The reflection from the manuscript 2 is guided to the lens 10 through the mirror 6 fixed on the carriage 4 and the mirrors 8 and 9 fixed to the moving mirror unit 7 to form the image on the CCD image sensor 12 on the circuit board. Numeral 13 shows a standard white board installed on the rear side of the edge of the platen glass 1 in the exposure scan direction, and provides the standard white signal at the start of manuscript reading.
With the stepping motor (not illustrated), the wire 15, and the pulleys 16 to 19, the moving mirror unit travels at a speed twice that of the carriage 4. The light path from the document 2 to the CCD image sensor 12 is kept constant in exposure scanning.
The exposure light 5 uses a green, commercially available fluorescent light in order to prevent white color emphasis and attenuation based on the light source. To prevent the fluorescent light from flickering, a 40 kHz high-frequency light source is used to turn on the light. Furthermore, a heater is used to keep the tube wall temperature constant and to achieve quick warming.
Beside mechanical causes of poor picture quality, the image reader or copying machine using the pickup system with a CCD image sensor provides some other causes including light-emitting spectrum distribution of the light source, mirror flatness, mirror vibration during its movement, modulation transfer function (MTF) of the mirror system and light-receiving sensitivity of the sensor. With respect to the color image pickup, there are other causes for poor picture quality including dichroic mirror transparent reflection characteristic and flatness/parallelism of the prism surface. MTF design of the mirror system is the most important for improved resolution.
The MTF of the signal from the CCD image sensor depends on these causes.
Comparison of poor MTF (due to distorted signal as shown FIG. 81 (a)) and better MTF as shown in FIG. 81 (b) demonstrates totally different reproduction of fine parts of image when image signal is coded with threshold (I) or (II). This indicates that correcting MTF for improved resolution is essential for reproduction of fine lines or characters.
There are two main methods to improve resolution for higher image quality: (1) a method to apply some measure in the time of coding picture signals and (2) a method to correct picture signals digitally.
The method (1) is illustrated in FIG. 82 (a). This method uses a low-pass filter to catch a variation in average value of the picture signal in digitizing the signal. This variation is used for a reference for determining a threshold in the digitization. This method allows the threshold to be floated and catch up typical variations of picture signal, resulting in better picture quality. The logic expansion of this method is known as an SWCC method.
As shown in FIG. 82 (b), the SWCC method makes a comparison signal by shifting the phase of picture signal to obtain digitized (binary) signal by making comparison with the comparison signal.
This method applies to analog signal processing; in fact, it is applicable to the case where shading correction is not required as a high-accuracy correction means, especially to the system which install a light shutoff board in front of lens or to the system which provides few noises.
However, the method cannot be applicable to the system which call for stability for temperature or good reproduction of picture or color image.
Method (2) is typically known as a differential operator which is described below.
In the case where taking a 2 by 2 pixel array like;
______________________________________ In the case where taking a 2 by 2 pixel array like; [1] [2] [3] [(a - d).sup.2 + (b - c).sup.2 ].sup.1/2 .vertline.a - b.vertline. + .vertline.b - c.vertline. [(a - b + c - d).sup.2 + (a - c + b - d)].sup.1/2 ##STR1## [4] .vertline.a - b + c - d.vertline. + .vertline.a - c + b - d.vertline. [5] (.vertline.a - b + c - d.vertline. + .vertline.a - c + b - d.vertline.)/2 [6] max(.vertline.a - b + c - d.vertline., .vertline.a - c + b - d.vertline. ) In the case where taking a 3 by 3 pixel array like; [7] [8] [(A + B + C - G - H - I).sup.2 + (A + D + G - C - E - I).sup.2 ].sup.1/2 .vertline.A + B + C - G - H - I.vertline. + .vertline.A + D + G - C - E - I.vertline. ##STR2## [9] U[1,0] + V[0,1] U = (C + 2F + I - A - 2D - G)/8 V = (A + 2B + C - G - 2H - I)/8 [10] E-min(A,B,C,D,E,F,G,H,I) [11] sign(B - H) .multidot. [min(A,B,C) - max(G,H,I)] [12] .vertline.E - A.vertline. + .vertline.E - C.vertline. + .vertline.E - I.vertline. + .vertline.E - G.vertline. [13] E - (B + f + h + d)/4 [14] E - (A + B + C + F + I + H + G + D)/8 ______________________________________
This method performs each calculation of (1) to (14), with a to d, and A to I being picture data. Formula (13) corresponds to a two-dimensional Laplacian calculation.
Examples of this method with the calculation are disclosed in Japanese Patent Publication Open to Public Inspection Nos. 43529/1978 and 42870/1981.
However, when applied to the system which uses a CCD image sensor to pick up images, these examples are not so effective with respect to the direction orthogonal to the linearly-arranged direction of a CCD image sensor pixel array.
One of the causes lies in the system shown in FIG. 80 using a charge-storing CCD image sensor for image pickup which provides a wider region in the secondary scan direction than in the primary scan direction, as shown in FIGS. 83 and 84. In addition, the aperture of the image sensor is apt to be longer than that in the primary scan direction, making effective resolution lower and inevitably ensuring MTF with respect only to a single cross section due to restrictions of lens treatment and yield. This makes the direction with a good MTF coincident with the primary scan direction, resulting in lower lens MTF in the direction of secondary scan than that in the direction of primary scan.
Accordingly, conventional MTF correction with corrected coefficients provides satisfactory result in the direction of the primary scan, but unsatisfactory result in the direction of secondary scan, or excessive correction in the direction of the primary scan. This emphasizes noises and the uneven surface of paper used, leading in conspicuous isolated noises. FIG. 85 (a) to (c) give an example of comparison of three cases in picture signal level.
This invention is related to the above description and allows proper correction of MTF along the both direction of primary and secondary scan.
An appropriate threshold value for multivalue coding an image signal undergone image processing has been hitherto been determined by generating a histogram by prescanning, or by determining a density range of the image and by multiplying the range by a predetermined factor. However, the former technique requires a duration for both prescanning and histogram generation, and to a disadvantage, results in a larger circuit configuration; the latter technique, though not requiring prescanning for histogram generation, fails to determine satisfactorily reasonable threshold value solely based on data resultant from the density range. Therefore, the object of the present invention is to provide an apparatus that is capable of determining an appropriate threshold value on the real time basis without performing the prescanning.
As shown in FIGS. 77 and 78, based solely on a color of a specific document, the result signal is unconditionally a single type of signal. Correspondingly, the gamma correction on a document image being read requires an image processing circuit for gamma correction, and, this means necessity of an arithmetic operation for every data set. According to the invention, therefore, a color discriminating means, more specifically, a plurality of storage means for color discriminating are provided, and each color discriminating means is endowed with different gamma characteristics, thereby one relevant discriminating means is selected per operation. This means that single relevant storage means is being referred to, and that high speed processing is realized.